1.Field of the Invention
This invention relates generally to an image reader suitable for use in facsimile machines, and more particularly to such an image reader having a locking mechanism capable of holding a platen in a state pressed against an image sensor.
2.Description of the Related Art
A facsimile machine for transmitting and receiving via telephone line images such as characters or figures described or illustrated on one or more original sheets generally comprises an image reader for reading images on the original as image information, a printer for printing the read image information on paper, and a transmission-reception device for transmitting and receiving via the telephone line the image information. The image reader includes an image sensor transversely disposed along a width of the original and a platen disposed to be pushed against the image sensor. In the image reader, the original carrying the images to be read is fed between the platen and the image sensor. The platen is then rotated to feed the original lengthwise so that images contained per line on the original are sequentially read by the image sensor. Thus, overall image information contained in the original is read by the image sensor. In this image reading manner, an accuracy in reading the image information is sometimes reduced when the original rises relative to the image sensor or when the image sensor becomes dirty.
To solve the above-described problem, the prior art has provided a locking mechanism for holding the platen in a state pressed against the image sensor. The locking mechanism comprises a pair of platen supports for rotatably supporting both ends of the platen respectively and a shaft disposed along the platen to connect between the platen supports. The locking mechanism is capable of rotatively moving upwardly and downwardly the platen supports and accordingly, the platen with the shaft as the center of rotation. Furthermore, the locking mechanism holds the platen supports at a lower limit position where the platen is pressed against the image sensor. In the reading of images, the platen supports are lowered to the lower limit position so that a platen roller is held pushed against the image sensor. Thus, the original can be prevented from abruptly rising. On the other hand, when the image sensor becomes dirty or when the facsimile machine has been clogged up with paper, the platen is manually lifted up together with the platen supports so that the platen is departed from the image sensor. Consequently, the image sensor etc. can be cleaned or the paper clogging the facsimile machine can be removed.
In the above-described image reader, however, the shaft is disposed along the platen to connect between the pair of platen supports. Accordingly, the shaft has approximately the same length as the platen. A space is required in order that the shaft may be disposed along the platen. This results in an increase in the size of the image reader and accordingly, that of the facsimile machine incorporated with the image reader.